What is Hemp?
Hemp is a natural material derived from the Cannabis sativa plant. Much like flax and jute, hemp is a ‘bast fibre’, meaning it comes from the inner bark or stem of the plant. It has diverse applications, from nutrition to construction, and can be processed into a wide range of useful end products.
Despite originating from the same plant species, different Cannabis sativa variants serve distinct purposes. Hemp is mainly used for industrial products, CBD (cannabidiol) is a compound with therapeutic properties, and marijuana contains THC (tetrahydrocannabinol), which produces psychoactive effects.
In this blog, we will be exploring the different types of hemp products, its benefits, challenges and more. So make sure you read all the way to the end.
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Historical Use of Hemp
Hemp is thought to have originated in Central Asia. Its earliest cultivation began in ancient China, where it was used for fibre as early as 2800 BCE. Archaeological findings suggest that hemp spread from this region to Europe and the Middle East through trade and migration over centuries.
In the UK, historical records indicate that hemp was used before Roman times, although specific records of its early use in Britain are limited. Folklore suggests that a Celtic princess named Cambri Formosa may have taught women to sew and weave with hemp around 373 BCE.
In the late 16th century, during the reign of King Henry VIII, it was so valued that farmers were mandated to grow it. They were required to plant a quarter of an acre for every 60 acres they owned. This was largely due to hemp’s utility in producing ropes and sails, essential for the British Navy. Hemp’s significance continued into the 17th century as it became a staple for maritime and textile uses.
However, the perception of hemp began to change over the years. By the early 20th century, hemp cultivation declined as cheaper imports became available. In 1928, the growing of hemp was banned altogether. This shift was influenced by concerns about cannabis use, which was associated with addiction and was seen as a societal threat.
Despite this shift, hemp’s industrial potential continued to be explored. For instance, in 1941, Henry Ford famously developed car body parts from hemp fibre and designed the car to run on hemp biofuel.
It wasn’t until the 1990s that attitudes started to shift again. Research distinguishing between the non-psychoactive components of hemp and psychoactive cannabis helped pave the way for legalisation. In 1993, hemp was again permitted to be grown in the UK, leading to a resurgence in interest.
In the 2000s, various legal adjustments regarding its classification were made. By 2018, regulations allowed the cultivation of hemp for industrial purposes, provided it contained less than 0.2% THC.
Since then, hemp’s popularity has grown steadily in the UK. Yorkshire has emerged as one of its largest cultivation regions. Today, hemp is used widely across industries, including paper, textiles, dietary supplements, and cosmetics. As demand rises, modern processing methods are being updated, paving the way for hemp’s continued relevance and growth in sustainable agriculture and industry.
Growing Hemp
Industrial hemp has very low levels of the psychoactive substance THC. In the UK, prospective hemp growers must undergo an official background check before applying for a controlled drugs domestic licence. This licence is required to ensure the cultivation complies with legal standards, particularly in limiting THC levels. Only certified low THC hemp seeds are allowed, and these can be planted directly into the soil.
Hemp is one of the fastest growing species on earth alongside bamboo. It is a hardy, annual crop that is naturally resistant to many pests and diseases, reducing the need for chemical pesticides. Hemp requires very little water and grows into a tall, bushy plant. Seed bearing hemp varieties tend to be shorter, typically reaching 1-2 metres in height, while fibre varieties can grow as tall as 1.5-4 metres. Their height helps them block sunlight from reaching weeds, so farmers do not need to use artificial herbicides or weed killers to control them.
The tall, bushy structure of the hemp plant can also provide shelter for pollinators like bees and butterflies while the flowers and leaves act as food sources. This helps to create habitats for various wildlife species that can enhance overall ecosystem diversity.
Additionally, hemp is often used as a rotational or break crop to improve soil health between other crops. Its deep roots reduce soil erosion and compaction, enhance water retention, and encourage microbial diversity, all of which are essential for soil fertility. As the plant breaks down, it returns valuable organic matter to the soil, enriching it for future crops and reducing the need for chemical fertilisers. It can also absorb harmful toxins like heavy metals from the soil, contributing to soil restoration in polluted areas.
Beyond its agricultural benefits, hemp cultivation contributes positively to the environment. It absorbs substantial amounts of carbon dioxide from the atmosphere, making it a carbon-sequestering crop that supports efforts to mitigate climate change.
Different Hemp Products
Hemp can be processed into a large number of different products. Its main forms include its fibre, seeds and oil.
Different parts of the hemp plant are used for different purposes. The fibre is extracted from tall skinny plants while the oil comes from the flowers of bushy plants.
Hemp can be processed into a large number of useful products. The key parts of the hemp plant include the seeds, the stalk, the leaves and flowers, and the roots. The stalk produces fibre, which comes from its outer layer, while the shivs (or hurds) are derived from its woody inner core.
Each of the key parts of the hemp plant serve various purposes, as listed below:
SEEDS
Animal feed
Beer
Cosmetics
Detergent
Dietary supplements
Flour
Granola
Hemp butter
Juice
Milk
Oil
Paint
Protein powder
Varnishes
STALK (Fibres, Shivs/Hurds)
Animal bedding
Automotive parts
Biochar
Biofuel
Bioplastics
Hempcrete
Cordage – Rope, Twine
Fibreboard
Insulation
Paper
Powder
Textiles – Clothing, Carpets, Upholstery
LEAVES and FLOWERS
CBD products
Compost
Essential oils
Mulch
Tea
ROOTS
Compost
Medicine
Natural dye
This diverse range of products demonstrates the versatility that the hemp plant has as a natural resource.
Types of Hemp Products in Construction
Hemp has gained attention as a sustainable, eco-friendly material in construction. It offers products that support energy efficiency and carbon reduction. From hempcrete for insulation to hemp fiberboard and hemp-based paints, these materials provide durable, non-toxic alternatives that promote healthier, more environmentally friendly building practices.
Hempcrete
Hempcrete is a biocomposite material which is made by combining hemp shiv (or hurds), lime based binder and water. It is a material that is lightweight, insulating, and has excellent thermal and moisture regulating properties. Since it is not a load-bearing material, it is typically used as insulation within timber-framed structures rather than as a standalone structural component.
There are three main ways to construct hempcrete walls:
Cast Hempcrete
For cast hempcrete, first a mixture of hemp shiv, lime binder and water is created. It can be either hand mixed in a bucket or mechanically in a pan mixer. The structural timber frame (stud wall) is constructed. To comply with building regulations, the frame may need to be covered in fire board or other membranes as it is accepted as a timber wall. In cases where plywood panels are recommended for racking strength, you can add diagonal bracing supports after consulting your engineers.
There are different options as to where the structural timber frame can go. It can be placed centrally or even flush to one side (perhaps internally to take heavy fixings or externally to take cladding). If placed in the centre or slightly off centre you do not need extra support as the hempcrete mix will engulf the frame and will not be able to move away from it. You will however require extra horizontal support battens if the frame sits only on one side. This is because the hempcrete mix will not have anything to cling onto and may move away from it.
The shuttering used is often OSB (Oriented strand board). It can be prefixed or it can go up gradually as you build the hempcrete in layers. You can also employ specialised shuttering systems.
The process is similar to that of rammed earth construction, which you can check out here:
A Guide to Rammed Earth Construction
Once all set up, the prepared hempcrete mix is collected in a bucket and poured into the shuttering. This is then distributed evenly and patted down lightly but firmly by hand or tamped with a timber rod. It is done lightly and not pressed in as over compaction can lead to the hempcrete drying slower and losing its insulating properties. The process is then repeated when the next bucket load of the hempcrete mix is ready to be poured in.
The shuttering is removed once the walls are dry. The finished walls are generally flat but have a textured surface, making them suitable for plastering or rendering.
This process is straightforward and accessible for self-builders, requiring minimal upfront costs for contractors to initiate a project. However, it does require skilled labour, and specialist contractors may face challenges in accessing and managing this labour force.
Additionally, cast hempcrete can be shaped into curves, offering further design flexibility.
The following images illustrate the cast hempcrete construction process:
Spray Hempcrete
This method requires a compact machine. The lime binder and water is mixed in the large drum of the machine and then tipped over into the pan mixer which keeps it agitated until it is ready to be pumped up the hoses. The hemp box of the machine is filled with hemp shivs and then blown dry down the hose to the nozzle allowance.
The binder is forced out of three nozzles by the compressed air and the nozzles are angled in towards a central stream of dry hemp. It can get messy if not careful but the output is quite controlled.
The structural framework is the same as with the cast hempcrete. You only require extra battens if the frame is on one side. This is so that the hempcrete clings onto the horizontal battens and avoids any possibility of separating from the frame.
The shuttering for sprayed hempcrete is very quick and can be as simple as hessian pinned to one side of the frame. After being sprayed the hempcrete is left overnight. The hessian is then peeled away the next day. After this the rest of the hempcrete sprayed from the other side of the wall. Cardboard can also be used as a shuttering material.
Once sprayed, you can use a piece of wood with lots of nails in it, essentially a long scratchy stick to run over the wall. You can have predetermined guide rails sprayed into the wall one at the top and one at the bottom. Old plate with wonky walls you can spray freehand and tidy up at the end with a nail float.
Crisp corners and flat walls can be achieved. There isn’t much waste hemp that drops on the floor. With thick, deep walls there will be hardly any but thin walls there may be more. The dropped hempcrete can be collected and cast into a shuttered wall.
The advantages are that spray hempcrete can be used in hard to reach places. The density of the hempcrete can be controlled by the machine. Although it is not quicker than cast hempcrete it does require less labour, which is easier for contractors to manage.
Sprayed hempcrete dries relatively quickly and is ideal for solid wall insulation.
Hempcrete Blocks
Hempcrete blocks are precast building materials created from a blend of hemp fibres mixed with lime and water. These blocks are joined together using a sand and lime mortar, which can be mixed conveniently in a cement mixer. They work effectively with a feature frame, which allows the blocks to be secured to the frame using stainless steel timber ties.
One of the advantages of hempcrete blocks is their versatility. They can be shaped and cut to any desired dimensions. The installation process is fast, and curves can be easily achieved with a nail float.
These blocks are already dry and readily accessible, requiring no specialised labour or tools. Their lightweight nature provides excellent thermal insulation by naturally regulating indoor temperatures and reducing the need for additional insulation layers.
Hempcrete blocks can also complement cast and sprayed forms of hempcrete. They can serve as permanent shuttering for sprayed hempcrete. One method is to use hemp blocks for the inside of the wall. As they are already dry the inside will be ready for plastering and then the exterior can either be cast or sprayed against.
Prefabricated Hemp Panels
These are pre-cast panels made from hempcrete. They are lightweight, durable, and sustainable panels that can be used for walls, roofs, and insulation in building projects.
You will also find some manufacturers have prefabricated wall systems using hemp. These not only help save construction time but also may help ensure consistent quality.
Hemp Wood
Hemp wood is a composite material created by compressing hemp fibres and resin. You can also find it in a biocomposite form, made with compressed hemp pulp fibres and a soy-based glue. Although it resembles traditional wood, it offers enhanced durability, resistance to warping, and a lower environmental impact in general.
It can be sanded, painted, and stained with oil-based stains which makes it suitable for a variety of applications, including interior construction, furniture, and flooring.
Hemp Rebar
Hemp rebar is a sustainable alternative to traditional steel reinforcement bars. It is made from a composite of hemp fibres and resins or thermoplastics. Although still in the experimental phase, it shows promise in providing structural support for concrete structures.
It offers several advantages over steel, including fewer carbon emissions, resistance to corrosion, cost-effectiveness, and the potential to extend the lifespan of structures.
Hemp Plastics
Hemp plastics are biodegradable materials produced from hemp-derived cellulose or fibres. These offer an eco-friendly alternative to petroleum-based plastics and can be suitable for various applications. To name a few – cladding, panels, furniture, fixtures, insulation, pipes, plumbing, floor, decking.
Hemp Fibreboards
These boards are engineered wood products made from compressed hemp fibres, providing a strong, lightweight, and sustainable alternative for furniture, cabinetry, and construction applications. They are moisture resistant and provide acoustic insulation.
Hemp Insulation
Hemp insulation is an eco-friendly product made from processed hemp fibres, offering high thermal performance, sound insulation, and a sustainable alternative to traditional insulation materials like fibreglass.
It is also breathable and readily available as batts, boards, or rolls. You can find it mixed with wool, polyester and other natural fibres such as jute or cotton.
Hemp Stuffing Wool
This is a natural insulation material derived from hemp fibres, used in bedding, upholstery, and insulation, known for its thermal properties, breathability, and resistance to pests. The hemp fibres trap air inside and give it great heat conductivity.
Hemp Roofing Materials
Hemp fibres can also be used to create durable roofing membranes or shingles, either on their own or as part of composite materials.
Hemp roofing materials include shingles and tiles made from hemp fibres, providing a renewable, durable, and insulating roofing solution that also reduces the carbon footprint of buildings.
Hemp Corrugated Sheets
These are another type of biocomposite that is a compressed hemp fibre sheet bonded with a sugar-based resin derived entirely from agricultural waste, such as corn cobs, oat hulls, and bagasse. These sheets possess properties similar to timber and may exhibit a silvery appearance when exposed to UV light.
They are lightweight, strong sheets that can be used in construction and packaging.
Hemp Plaster
Hemp plaster is made from a mixture of hemp shivs (or hurds), lime, and water. It provides excellent insulation, breathability, and moisture control in construction.
You can also have hemp and clay plaster as a finish for both internal and external walls.
Hemp based Paints and Coatings
These natural paints, varnishes, coatings and sealants are derived from hemp seed oil. They are non-toxic, biodegradable alternatives that offer good adhesion and durability. They are free from harmful chemicals and volatile organic compounds.
Hemp Carpets and Textiles
Hemp carpets and textiles are eco-friendly floor coverings and fabrics produced from hemp fibres. They can be applied in interior design. They are known for their durability, natural resistance to mould and pests, and sustainable production process.
Hemp Geotextiles
Hemp geotextiles are woven or non-woven fabrics made from hemp fibres. They are primarily used in landscaping and road construction. They help stabilise soil and promote plant growth by allowing water and nutrients to pass through.
Benefits of using Hemp
Hemp has a great number of advantages:
Sustainable
Hemp is a renewable resource as it grows quickly and manufacturing it is a low energy consuming process. Hemp plants also sequester a large amount of carbon dioxide during their growth. Additionally hemp based materials are biodegradable, meaning they don’t contribute to long-term waste or pollution at the end of their lifecycle. They can often be sourced locally, further reducing transportation emissions.
Energy efficient
Hemp retains heat and has excellent insulating properties. It keeps the indoor temperature constant and reduces the need for artificial heating and cooling.
It also allows moisture to pass through it, which helps prevent mould growth and improves indoor air quality. Hemp materials provide excellent moisture buffering capabilities and airtightness, allowing for effective moisture management without trapping humidity, which is crucial for maintaining indoor air quality.
Hemp offers great acoustic insulation as it absorbs and dampens sound waves.
Structure
Although it is lightweight material it can be used to achieve monolithic construction. The process can be quite low tech depending on the type of hemp product used. It can be moulded into various shapes, making it suitable for different types of projects.
Hemp products are also strong and can last for decades or even centuries when well-maintained. It’s also resistant to cracking and can self-heal minor fissures.
Fire and Pest Resistance
It offers passive fire resistance and just like timber it chars. The lime covering it, in terms of hempcrete, helps it not ignite. It does not transmit heat very quickly through the material.
No toxic coatings or linings are needed, eliminating harmful off-gassing.
Hemp has a natural resistance to pests and mould.
Healthy
Hemp does not contain toxic substances such as formaldehyde or volatile organic compounds (VOCs). Its breathable nature reduces exposure to harmful chemicals, enhancing indoor air quality.
Scalable
Hemp can be mass-produced, making it a viable option for large-scale construction.
Challenges of using Hemp
There are also a number of challenges, when working with hemp:
Structure
Hemp by itself has very limited load bearing properties on its own. It does require a structural framework to strengthen it, which may add to overall construction costs and complexity.
Cost and availability
Hemp based materials may be more expensive than conventional building materials like concrete and fibreglass, largely due to limited production and processing facilities.
While the popularity of hemp construction is growing, it’s still not as widely available in many regions as other materials. This can lead to supply chain delays and higher transportation costs.
In some regions, legal restrictions or building regulations may not fully support the use of hemp, causing issues.
Long curing time
Hemp takes longer to cure than traditional concrete. This extended curing time can delay construction timelines, especially in projects where rapid completion is necessary.
Weather sensitivity
While hempcrete is breathable and resistant to mould, if not adequately protected or sealed, it may absorb excess moisture, particularly in very wet environments. This may lead to potential degradation over time if exposed to harsh weather without protection.
Limited expertise
Since hemp construction is still relatively niche, finding builders and contractors with experience in working with hemp materials may be more difficult. This could result in higher labour costs or unsatisfactory results if the installation is not done correctly.
Books
Here are some recommendations for some hemp related further reading for you to indulge in:
You Might Also Be Interested In
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Conclusion
Hemp is a remarkable building material with a long history and significant potential in modern sustainable construction. Its benefits include excellent insulation, low environmental impact, and carbon sequestration, making it an attractive alternative to traditional materials. Although it does face challenges like limited load-bearing capacity and availability, growing awareness and technological innovations are helping to overcome these barriers.
All in all, by incorporating hemp into our construction practices, we can develop innovative, eco-friendly solutions that promote a sustainable future.
We hope this post has deepened your understanding of hemp as a natural material. Stay tuned for more in depth posts in our natural materials series.
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Author
Written by Valanne Fernandes, a Part 2 Architecture graduate. Valanne is a content creator with First In Architecture, spending her time researching, writing and designing inspiring new content for the website.
So educative